1. Field of Invention
This invention relates generally to gas administration apparatus, e.g., anesthesia machines, and more particularly to interlocks or exclusion systems for use with such apparatus having multiple gas flow units, e.g., vaporizers, to prevent more than one gas flow unit from being opened at the same time.
2. Description of Related Art
It is common practice for an anaesthesia apparatus to have mounted on it two or more separate vaporizers, each arranged for delivering different volatile anaesthetic so that the same basic anaesthesia apparatus can be used during a series of surgical operations to meet the needs of different patients.
In U.S. Pat. No. 4,307,718 (Schreiber), which is assigned to the same assignee as this invention and whose disclosure is incorporated by reference herein, there is disclosed an interlock device for a pair of vaporizers of an anesthesia machine. Each vaporizer includes a rotary dial for establishing the vapor concentration provided. The interlock device insures that one vaporizer is closed whenever the other is open and comprises a pair of reciprocable pins and a cooperating pivotable lever. Each pin is arranged to be extended into a cam recess in the vaporizer dial by the pivoting action of the lever. Rotation of one dial automatically causes the pin located therein to move out of the cam recess and into contact with the lever. This action pivots the lever and causes it to contact the other pin to extend the other pin into the recess in the associated vaporizer dial, thereby locking the dial closed.
The assignee of this invention has sold anesthesia machines, e.g., the Narkomed® 2A device, making use of three non-removable vaporizers and an exclusion or interlock system for preventing more than one such vaporizer to be opened at any one time. The exclusion system used in that machine basically comprises three pivotable bars, one long one and two short ones. The two short bars are located end to end in front of the long bar. Each bar is arranged to pivot in a horizontal plane about its midpoint. The two short pivot bars are located immediately behind the rotatable caps of three side-by-side, non-removable vaporizers. Each vaporizer cap includes a cam slot or recess in which one end of a respective reciprocating pin is located. The free end of the pin for the leftmost vaporizer is located adjacent the leftmost end of the left side short pivoting bar and is arranged to engage it when the leftmost vaporizer is used. In still a similar manner free end of the pin for the rightmost vaporizer is located adjacent the rightmost end of the right side short pivoting bar and is arranged to engage it when the rightmost vaporizer is used. The free end of the pin for the middle vaporizer is located adjacent the rightmost end of the left short pivoting bar and the leftmost end of the right side short pivoting bar to engage both of those ends when the middle vaporizer is used. The long bar includes a pair of pins or set screws attached to each end and projecting outward therefrom. The pin on the leftmost end of the long pivoting bar is arranged to be engaged by the leftmost end of the left short pivoting bar. In a similar manner the pin on the rightmost end of the long pivoting bar is arranged to be engaged by the rightmost end of the right short pivoting bar. Operation of that exclusion system for each of the three vaporizers is as follows: all of the vaporizers should be off, i.e., their caps turned to the off position, before any particular vaporizer is opened. For example, if the rightmost vaporizer is to be used, the rotation of its cap causes the pin associated with it to move rearward, thereby engaging the rightmost end of the right short pivoting bar. This action pivots that bar counter-clockwise to bring its rightmost end into engagement with the projecting setscrew on the rightmost end of the long pivoting bar, thereby causing that bar to pivot counter clockwise. The pivoting of the right short bar brings its left end into engagement with the pin for the middle vaporizer, thereby holding it in position whereupon the pin is located within the cam recess of the vaporizer cap, to thereby prevent it from being turned (opened). The pivoting of the long bar brings its setscrew on its left end into engagement the leftmost end of the left short pivoting bar, thereby pivoting the left short bar counterclockwise, whereupon it engages the pin for the leftmost vaporizer, thereby holding that pin in position within the cam recess of the leftmost vaporizer cap to prevent the cap from being turned (opened). If the leftmost vaporizer is to be used, all of the vaporizers must be turned to the off position. Then the leftmost vaporizer can be opened. The operation of opening the leftmost vaporizer is similar to the operation of opening the rightmost vaporizer, except that the two short bars and one long bar are pivoted in the opposite directions to prevent the pins from the middle and rightmost vaporizers from exiting their respective cam recesses. If the middle vaporizer is to be used, all of the vaporizers must be turned to the off position. Then the middle vaporizer can be opened. In particular, the cap of the middle vaporizer is rotated to an open position, whereupon its pin is moved backward to thereby engage the rightmost end of the left short pivoting bar and the leftmost end of the right short pivoting bar. This causes the left short bar to pivot counterclockwise and the right short bar to pivot clockwise. The pivoting of the left short bar counterclockwise causes its left end to engage the pin associated with the leftmost vaporizer to hold it in position within the cam recess of the leftmost vaporizer cap to prevent that cap from being turned. In a similar manner, the pivoting of the right short bar clockwise causes its right end to engage the pin associated with the rightmost vaporizer to hold it in position within the cam recess of the rightmost vaporizer cap to prevent that cap from being turned.
In United Kingdom patent specification No. 1,385,670, there is described a gas administration apparatus on which one or more gas flow units can be mounted in a removable plug-in fashion.
In United Kingdom patent No. 2,052,271, there is described an interlocking system which prevents two different anaesthetic being delivered to a patient at the same time or otherwise becoming mixed. This known interlocking system includes pins associated with each vaporizer which, when its concentration dial is moved from the off position, causes the pins to extend outwardly and block the movement of corresponding pins on immediately adjacent vaporizers thereby preventing the concentration dials of these other vaporizers from being operated. With this arrangement it is impossible to switch more than one vaporizer into a gas circuit at any one time. While this known interlocking system works well when there are two or more units arranged side-by-side, if the middle unit of, for example, three units is removed for any reason then the interlocking action of the first unit cannot be transmitted to the third unit and vice versa. One solution to this problem involves using non-functional (dummy) second units or merely applying warning labels to indicate that no interlocking system is available.
In U.S. Pat. No. 4,759,358 (Gregory) there is disclosed an interlock system for use with two or more gas flow units (vaporizers) when mounted in plug-in fashion on the back bar of an anaesthesia machine. Each unit includes a rotary cap, which when moved from an off to an operative position admits to the unit a gas from a supply provided by the apparatus. The interlock system includes at least one pin associated with each gas flow unit which, when the rotary cap is moved towards its operative position, extends outwardly from the unit to engage and move a spacer mounted for sliding movement on the apparatus between adjacent units towards a similar adjacent unit thereby to prevent the rotary cap of the similar adjacent unit being moved towards its operative position.
Other United States Patents disclosing anesthesia apparatus including interlocks/exclusion systems for preventing more than one vaporizer from being opened at any one time are: U.S. Pat. No. 4,463,754 (McDonald); U.S. Pat. No. 4,493,318 (Mohr et al.); U.S. Pat. No. 4,932,398 (Lancaster et al.); U.S. Pat. No. 5,520,168 (Whitaker); U.S. Pat. No. 5,657,747 (Holliday); and U.S. Pat. No. 6,302,104 (Kronekvist).
While the above interlocks/exclusion systems may be generally suitable for their intended purposes, they exhibit one or more of the following drawbacks, e.g., complexity, ease of use, limited number of vaporizers that can be accommodated, etc.
All references cited herein are incorporated herein by reference in their entireties.